1. Field of the Invention
The present invention relates to an exposure apparatus that exposes a substrate in a status in which the space between the projection optical system and the substrate has been filled with a liquid, and to a device manufacturing method that uses this exposure apparatus.
2. Description of Related Art
A semiconductor device or a liquid crystal display device is manufactured by the technique known as photolithography, in which a pattern formed on a mask or reticle (hereunder called “reticle”) is transferred onto a substrate such as a wafer or a glass plate. The exposure apparatus used in this photolithography process has a reticle stage that supports a reticle and a substrate stage that supports a substrate, and it transfers a reticle pattern to a substrate via a projection optical system while sequentially moving the reticle stage and the substrate stage. In recent years, higher resolutions for projection optical systems have been in demand to deal with further high integration of device patterns. The resolution of the projection optical system becomes higher the shorter the exposure wavelength used and the larger the numerical aperture of the projection optical system. For this reason, the exposure wavelengths used in the exposure apparatus are becoming shorter each year, and the numerical apertures of projection optical systems are also increasing. In addition, the mainstream exposure wavelength at preset is the 248 nm of a KrF excimer laser, but a shorter wavelength, the 193 nm of an ArF excimer laser, is also coming into practical application. In addition, when exposure is performed, the depth of focus (DOF) is also important in the same way as the resolution. The resolution Re and the depth of focus δ are expressed by the respective equations below.Re=k1·λ/NA,  (1)δ=±k2·λ/NA2,  (2)
Here, λ is the exposure wavelength NA is the numerical aperture of the projection optical system, and k1 and k2 are process coefficients. Based on Equation (1) and Equation (2), it is apparent that when the exposure wavelength λ is made shorter to increase the numerical aperture NA in order to increase the resolution Re, the depth of focus δ becomes narrower.
When the depth of focus δ becomes too narrow, it becomes difficult to match the substrate surface to the image plane of the projection optical system, and there is concern that the focus margin during the exposure operation will be inadequate. Therefore, the liquid immersion method disclosed in PCT International Publication No. WO99/49504, for example, has been proposed as a method of effectively shortening the exposure wavelength and widening the depth of focus. This liquid immersion method fills the space between the lower surface of the projection optical system and the substrate surface with a liquid such as water or an organic solvent, and it uses the fact that the wavelength of the exposure light in liquid becomes 1/n in air (n is normally approximately 1.2 to 1.6 at the refractive index of the liquid) to increase the resolution as it expands the depth of focus by approximately n times.
In any case, in a status in which the space between the substrate surface and the end face of the optical member that is most on the substrate side of the projection optical system is filled with liquid, vibration produced by the movement of the substrate stage that supports the substrate is transmitted to the optical member at the terminating end thereof via the liquid, and there is a possibility that the pattern image projected onto the substrate via the projection optical system and the liquid will deteriorate.
Furthermore, in the aforementioned prior art, in order to form a liquid immersion region, a nozzle member that has a liquid supply port and a liquid recovery port is used to perform liquid supply and recovery, but when liquid penetrates into the gap between the nozzle member and the projection optical system, there is a possibility of nonconformities such as rust being produced on the barrel that holds the optical members that comprise the projection optical system or the optical members dissolving. It is also conceivable that liquid will penetrate to the interior of the barrel, and there is a possibility of the above nonconformities occurring in that case as well.
In addition, due to the effects of the liquid that has penetrated, there is a possibility of a nonconformity occurring whereby, for example, the optical member that is most on the image plane side in the projection optical system deforms or vibrates, albeit slightly, leading to deterioration of exposure accuracy and measurement accuracy.